Numerical Investigation and Optimization of the Flow Characteristics of Bend Pipe with Different Bending Angles
Round 1
Reviewer 1 Report
Dear Authors:
I have the following questions and comments to be addressed for your submitted manuscript.
Please add the novelty/major contribution of your study (1-2 sentences) in abstract.
In Figure 7, velocity distribution at bend angle of 120 degree and 180 degree are similar. However, why the velocity distribution at 180 degree and 120 degree in Figure 8 is different. In Figure 8, the velocity is tend to be constant along the tubes at 180 degree while there is significant changes in velocities at 120 degree? Please explain or double check it.
In Figure 6, what's the unit or scale bar for the pressure? Please the add the label for the different colors.
How did you validate your simulation results? Please add experimental results or previous results that can verify the accuracy of your models.
In line 382, H/D=thick diameter ratio, where H is the thickness of the flow deflector. What's the length and structure of flow deflector? Is the flow deflector similar to the baffle? How is the flow deflector installed in the different bending angles? Add more details for Figure 11.
Description between 326 to 329 is not accurate. There is no velocity cloud in Figure 6. Please make correction.
I am looking forward to receiving the revised manuscript with modification.
Best regards,
Reviewer
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
After reading the revised version, the reviewer became more convinced that the authors did not understand the Navier-Stokes equation at all. If those who know even a little fluid mechanics see Eq.(1) and Eq.(2) of the revised manuscript, the authors’ ignorance of fluid mechanics is obvious for them. The authors have no basic knowledge of mathematics regarding vector operations. Eq.(1) is not wrong but the use of parenthesis for vector u is strange. The left hand side of Eq.(2) is absolutely wrong. The authors don’t know that there are two kinds of vector production; the one is the scalar product and the other is the vector product. This kind of math is high school level. It is also doubtful whether the authors understand the nabla operator and Laplacian operator. This work is an example that it is possible for users of commercial software to derive interesting results though they do not have the knowledge of basic theories. However, if the paper was published in the revised form, it would be a big shame for the journal due to the wrong description of basic equations. As the reviewer pointed out before, this mistake does not affect calculated results, because wrong equations shown in the paper were not used in practical calculation. The reviewer suggested in the first review that Eqs (1) and (2) are cut to hide the authors’ ignorance. If the authors wish to describe the continuity equation and momentum equation (Navier-Stokes), consult someone who know fluid mechanics and describe equations with no mistake.Author Response
Please see the attachment.
Author Response File: Author Response.pdf
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
The authors have conducted a detailed analysis of flow through bent tubes. The computations and analysis are sound and the results are consistent with what is already known. Unfortunately, this is a flow for which the physics is which is well understood. And there have been empirical measures for distance downstream of a bend for flow to become uniform again. So there is really nothing significant or new in this paper. Therefore, I can't recommend publication of this work.
Reviewer 2 Report
Major comments:
Page 4 to 5: The Section 2.2 (Governing equation) should be totally rewritten. It seems to the present reviewer that the authors do not fully understand the theory of fluid mechanics and modelling of turbulent flows. First, the expression of Eq. (2) is wrong. This mistake is not careless, but comes from their inadequate knowledge. The most important governing equations for this kind of work are RANS (Reynolds-Averaged Navier-Stokes Simulation) model and definition of eddy viscosity. It makes no sense to display the continuity equation and Navier-Stokes equation instead of RANS model. Also it is strange that the reference (28) is cited for the NS equation (Navier-Stokes). The NS equation is explained in ordinary standard text books of fluid mechanics. If the authors want to explain the governing equations in this paper, they should start with RANS model on which the software Fluent is based. The description of the k-epsilon model should follow the definition of eddy viscosity, If it is difficult for the authors to modify the Section 2.2 based on the reviewer’s comments, another option is to cut the description of Eqs.(1) and (2). Instead, the authors should describe the details of the commercial software FLUENT used in this work.
Minor comments:
Page 2, line 31: what is the bending coefficient? It should be briefly defined.
Page 3, line 7: The first sentence “The schematic diagram…” is not complete. The sentence should be “The schematic diagram……is shown in Fig.1”.
Page 5, 7 and 8: The meaning of the sentence “In addition ,,,,,,,, to 10-5” is not clear. What does the number 10-5 mean ?
Page 6: The word “instability” is often used. What does this word mean in this phenomenon ?
Figs.8, 9, 14, 15, 16: The color difference between the plotted points is not clear, particularly red and blue.
Page 12, line 7 from the bottom: the symbol after the word “where” is missing.
Page 12, line 4 from the bottom, the symbol after the word “of” is missing.
Page 12, line 2 from the bottom: symbols after “at” and “the” are missing.
Page 13, line 6 from the bottom: the symbol after the word “of” is missing.
Page 14, line 7: The symbol after the word “of” is missing.
Page 14, line 8: The symbol after the word “when” is missing.
A figure of relation between zeta vs H/D corresponding to Fig.12 should be shown.
Reviewer 3 Report
Dear Authors:
I am glad to read and learn from your article. Please see the following suggestions and comments:
In Table 1, missing the relative error for the No. 6.
For equations, please add units for the symbols.
In introduction, please add some background on the effect of the different shapes of pipes on pressure, velocity distributions and heat transfer that readers understand the angles and shapes for the tubes/pipes using the suggested references.
Ji, Y., Wilson, C., Chen, H. H., & Ma, H. (2011). Particle shape effect on heat transfer performance in an oscillating heat pipe. Nanoscale Research Letters, 6(1), 1-7.
Qian, X.; Yang, Y.; Lee, S.W. Design and Evaluation of the Lab-Scale Shell and Tube Heat Exchanger (STHE) for Poultry Litter to Energy Production. Processes 2020, 8, 500.
Bezyan, B., Porkhial, S., & Mehrizi, A. A. (2015). 3-D simulation of heat transfer rate in geothermal pile-foundation heat exchangers with spiral pipe configuration. Applied Thermal Engineering, 87, 655-668.
In Figure 1, Authors mentioned it is 3D model. But, 3D model should be looks like models in Figure 2. Please change your title of Figure 1. In addition, there is no description for Figure 1.
Why did you particularly selected bending angle of 5, 30, 60, 130, and 180?
In Figure 6, please indicate the positions of these cross-sections at various bending angle. Starting point, middle or ending point of the bending section?
Same as Figure 7, what is 0D, 1D until the 10D?
In Figure 8, why you analyzed only few distances different than the Figure 7?
Section 6. Patents are not appropriate.
In 4. structure optimization, please add the five HD and five LR. There should be more discussions on the RB, D and H in Figure 11 because these parameters are not very clear and hard to determine in the real world.
In section 4.1, some sentences are not complete sentences. Please revise.
In conclusion, please discuss more details based on the selected angels, thick-diameter ratio and length-diameter of the flow deflector.
In the methodology, please mention the commercial software Fluent.
I am looking forward to review the revised version.
Sincerely,
Reviewer
